Circadian rhythms are a class of biological rhythms whose period is close to 24 hours. These rhythms appear at all levels of eukaryotic organization and, in mammalian physiology, there are few systems that are not affected in some way by circadian rhythmicity. These rhythms are controlled by biological clocks: circadian pacemakers, localized to restricted portions of the neuroendocrine system, which act to time many diverse behavioral rhythms. Another role for circadian pacemakers is the synchronization, or entrainment, of distributed oscillators located throughout the organism. Several studies have suggested that desynchronization between multiple circadian rhythms can have profound effects on human physiology, affecting mental health and resulting in such well known phenomena as: "jet-lag". However, while circadian pacemakers have been identified in multiple sites within the neuroendocrine axis, very little is known about the anatomy and physiology by which circadian pacemakers exert their effects on overt behaviors, or how information from multiple circadian pacemakers is integrated within the nervous system. In this study, the anatomy and physiology of pacemaker expression and integration will be investigated in two invertebrate model systems, Aplysia californica, and Bulla gouldiana, using neuroanatomical and neurophysiological techniques. In this study I wish to determine: 1) the anatomical pathways and physiological mechanisms by which circadian pacemakers modulate locomotor command elements, and 2) the effect of desynchronization between two circadian pacemakers upon central neural elements, and the behavioral consequences of this desynchrony. The circadian system of A. californica and B. gouldiana is formally quite similar to that of the rodent, so the information gained in this study may provide insight into the general cellular mechanisms behind the central processing of pacemaker information and the expression of circadian behaviors.